SMD Resistor Solutions above One Watt
This product highlight will discuss resistor solutions for applications with requirements above 1 watt. Historically, for a resistor to achieve 2 watt and higher power ratings it would require multiple ceramic based chips.. There are several new approaches to handling these higher power requirements and each approach has its advantages and disadvantages. It is important to understand these pros and cons to help customers design in the right product for their design goals.
Using several ceramic based chip resistors to accomplish a 2 or 3 watt power rating is still viable solution for some applications. If board space is plentiful and there are no issues with thermal expansion stress, simply using 2 or 3 general purpose chip resistors will always be the cheapest alternative. However, if thermal stresses or board flex is a potential issue, only 1210 size chip resistors and smaller are recommended. General purpose 1210 size chip resistors are only rated for 1/3 watt power rating, meaning it would require 6 parts in parallel to achieve a 2 watt power rating. While a two and even three resistor solution can sometimes be the best option, rarely is a 6 part solution a good idea when there are single components that can dissipate 2 watts safely and without risk of cracking or solder joint failure.
Ceramic Based High Power Chip Resistors
Recently many manufacturers have developed chip resistor series with higher power ratings. Stackpole has several series to offer: RMCP thick film high power chips, RNCP anti-sulfur high power chips, and the RHC2512 high power chip resistor with low heat rise. Each series has some advantages and disadvantages compared to the others. Before discussing those it should be noted that when using high power resistors of any kind, even though the resistor may be rated for a certain power level, it’s important that the part be kept in its normal operating temperature range meaning hot spot and terminal temperatures of less than 105C.
The RMCP is the product of choice if thick film technology is desired, such as for high moisture applications. For chip resistors with higher power ratings, there are also certain sizes and resistance values where the RMCP is the only option. Many customers will choose the RMCP because it is the closest match to our standard RMCF. The RHC is limited to only a 2512 size, but is a very popular choice for many 1 and 2 watt power requirements where its superior thermal characteristics are key. The RHC is the most expensive of these products. Another high power chip resistor series available from Stackpole is the RNCP, however it is capable of a maximum of 0.5W in a 1206 package.
Surface Mount Wirewounds
Surface mount wirewounds are the product of choice when the application requires high power handling and there is potential for mechanical or thermal stresses which might cause ceramic based resistors to fail. The compliant terminations of the SM series allow the terminations to bend and flex with the PCB eliminating the possibility of parts cracking or solder joint failure. In addition, surface mount wirewounds will inherently yield lower PCB temperatures, similar to the RHC, and offer 3 and 4 watt sizes. However, the SM series is available in limited resistance values. The highest resistance value available for the SM2615 1W device is 1K ohms and for the SM8035 4 watt device it is 5K ohms. Surface mount wirewounds are also relatively expensive compared to ceramic based chips, with pricing ranging from $0.33 to $0.90 each.
HPC High Power Chip
The HPC12 high power chip is the only surface mount resistor capable of 5 watts power handling in free air over a wide resistance value range. The HPC’s metal housing and leads are compliant and eliminate the concern for solder joint integrity or parts cracking. The design of the HPC raises the resistance element off of the PCB which aids in lowering board temperatures. Finally, the HPC12 can dissipate up to 15 watts continuously with proper airflow. The HPC is the most expensive of the high power resistor options, with pricing ranging from $0.90 to $1.75 each.
For more information about Stackpole products, contact Stackpole Electronics, Inc. at
Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now affiliated with Akahane Electronics, Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Hong Kong and Japan; and sales offices in Tokyo, Hong Kong and Taiwan.